Several alarm systems are in use wherein a break-in activates an automatic dialer mechanism sending a signal to a remote monitoring station. The nature of this arrangement automatically identifies the dwelling placing the call, whereupon appropriate security measures are taken. Since the link between the dwelling phone and remote station already exists or is easily established, it would seem desirable to use the same in providing two-way emergency communication. If an emergency arose, it would then be possible to provide two-way communication over the link allowing the nature of the emergency to be assessed.
However, merely placing an active microphone and active speaker on an established telephone link could create problems such as acoustical feedback, hum pickup or instability.